"The work is mysterious and important".
In 'Severance', where workers have their personal lives surgically divided from their work time, main characters work in a macro data refinement department… whatever that means. Basically, their job is to to parse endless flows of numbers in order to decide which one of them are "scary", "sad", "angry" or "happy" enough and mark them correspondingly.
While it's unknown how exactly the workers should define the numbers, they somehow manage to tune in with their feelings when it comes to certain numbers. What remains a mystery is basically everything else. What do these numbers mean? What does deleting them do?
There are several theories regarding the meaning of numbers in Lumon. Some fans suggested that by marking the numbers, macrodata refiners essentially kill people, or some other creatures. The employees themselves have guessed that they might be doing a job as dull as removing swearwords from movies. But one theory posted on Reddit appears to be a lot more satisfying when you think about it.
In the show, Lumon founder Keir Eagan identified four tempers: woe, frolic, dread, and malice. Basically, these tempers correspond with emotions the workers are supposed to feel after encountering certain numbers, so chances are that Lumon uses refiners to help a mysterious machine learn more about intelligence – not only artificial, but also human.
If the fan theory turns out to be right, then the numbers essentially have no meaning, with the actual goal being to study the way refiners classify them. However, that's not the end of it:
"The buckets are labeled WO, FC, DR, MA. The four tempers are Woe, Frolic, Dread, and Malice. In this fan theory, the numbers represent parts of Kier's memories related to Dread. The MDR refiners are being used to understand how raw cognitive data maps onto human consciousness in accordance with the "four tempers" theory." – /lord_braleigh.
With season 1 leaving fans with more questions than answers, at least they know that season 2 is coming, albeit the release date is yet to be confirmed.